The increased awareness of health benefits associated with dietary fiber has created a demand for dietary fiber supplements (DFS) for food items that is projected to equal 600 million pounds by 1992. This is a substantial increase from the current DFS use of 150 million pounds per year. Dietary fiber is generally considered to be that part of plant-like material which is resistant to mammalian digestive enzymes such as hemicellulose, cellulose, lignin, pectin, and other polysaccharides, such as gums, mucilages and b-glucans.
There are two basic classes of dietary fiber--soluble and insoluble. The insoluble fibers are used as supplements in bread, hamburger rolls, cookies, snack foods, pasta, pizza, etc., whereas the soluble fibers find application in liquid type food products, such as soft drinks, yogurt, salad dressings, spreads, ice cream, etc.
The functional role of dietary fiber supplements are many. These include health-related properties, such as bile acid adsorption, adsorption of toxins in the gut, low calorie bulking agents and water adsorption which cause rapid intestinal transport and increased fecal weight. The beneficial results of adding soluble and insoluble fiber to other food components are many; some of these include, adding bulk, mouth feel, moisture retention, emulsion stabilization, viscosity control.
While the scientific explanations of all the health impacts of dietary fiber consumption are yet to be developed, evidence of the beneficial effects of dietary fiber was reported by the Ad Hoc Expert Panel on Dietary Fiber in Physiological Effects and Health Consequences of Dietary Fiber, S.M. Pelch (ed.), Fed. Am, Soc. for Exp. Biology, Bethesda, MD, June(1987). It recommended that adults consume 20 to 35 g/day. However, since some dietary fibers, particularly those high in phytic acid, can also adsorb key minerals such as Ca or Zn, too much of such dietary fibers can lead to mineral deficiencies.
There are many sources of dietary fiber. It can be found in cereals, cereal brans, fruits, vegetables, and plant stems. There are many processes for the isolation of dietary fiber preparations from natural sources. The usual approach is to recover a dietary fiber from a seed hull or tuber by removing toxins, starches, oils, etc. or improving the mouth feel by some processing step. The fiber may be enriched by mechanical, chemical, or enzymatic means. Generally these processes do not add new functional properties to the fibers and it is necessary to rely upon other different fiber sources, sugar beet, wheat bran, pea hulls, soy hull, oat bran, etc. to get additional desired properties.
One of the simplest approaches for isolating dietary fiber is to simply form an aqueous slurry of the ground outer seedcoats of a legume, such as peas, to dissolve the protein and sugar and then to filter and t dry the insoluble fiber. The resulting product is suggested for use as a fiber enhancer in bread, muffins, or pasta.
In another process, dietary fiber is separated from vegetables, such as asparagus, by a series of steps involving boiling in water, washing with water, dewatering and drying. The product is suggested for use to adsorb mutagens.
In the process of Nonaka and Headly U.S. Pat. No. 4,757,948 a high total dietary fiber (over 80%) is obtained from corn fiber from a wet mill operation by a sequence of sifting the course fibers, roll milling and sifting again.
In a more involved process, a wheat bran dietary fiber is obtained by mixing a slurry of bran at pH 5.0 for 6 to 10 hours at 50.degree. C. to 60.degree. C. The natural phytase in the bran removes the phytic acid, which normally will adsorb metals. Then the protein and starch are removed by addition of protease and amylase enzymes; the enzymes are deactivated by heating the slurry to 95.degree. C. to 100.degree. C. for 1 hour. The fiber is washed, dewatered and dried. The product has more than 70% dietary fiber with less than 0.5 wt% phytic acid, negligible Fe, Ca or Zn adsorption, improved water swelling, water retention, and bile acid adsorption.
In the process of the Bommarito U.S. Pat. No. 4, 795, 633 sugar beet fibers are processed in a 5% acetic acid solution containing a bacteriacide and ascorbic acid as an antioxidant at 38.degree. C. to 60.degree. C. The dietary fiber containing pectin, cellulose, hemicellulose, lignin, protein and minerals is pressed and dried. This process removes natural toxins such as nitrates, oxalates, and saponins. The fiber is said to be effective in weight loss programs for obese people and treatment of irritable bowel syndrome.
In order to overcome the grittiness of cereal brans when incorporated in cereals, the Fulger U.S. Pat. No. 4, 759, 942 suggests grinding bran to 5 to 100 microns instead of the usual 150 to 840 microns improves mouth feel. The Chigurupati U.S. Pat. No. 4,735,814 overcomes the gritty mouth feel and mineral adsorption of dietary fiber by coating the bran with flour in a fluidized bed.
A dietary fiber product made from a fine suspension of wheat bran which is easily suspended by shaking in drinks and which is said to have an excellent mouth feel is made by the process of the Chavkin and Mackles U.S. Pat. No. 4,731,246. In the process 40-mesh bran is heated in water at pH 3.5 to 5.0 with 0.2% aluminum magnesium silicate for 20 to 60 mins at 80.degree. to 100.degree. C. and then cooled and subjected to sheering stress in a colloid mill.
An approach for enhancing the mouth feel of dietary fibers from any source is to coat them with soluble dietary fiber, such as alginates, gums, or pectin, which keeps the caloric value low for the treated fiber.
Other approaches include the process of the Fulger and Bradburg U.S. Pat. No. 4,500,558 which uses an extruder to heat treat the bran with its starch to coat the bran at 180.degree. C., the extrudate is then milled to give an acceptable mouth feel and moisture retention. In the process of Kickle, et al U.S. Pat. No. 4,181,747 a 3 to 6% slurry of seed hull fiber at pH 2.5 to 5.0 (adjusted with H.sub.2 SO.sub.4) is heated to 65.degree. to 77.degree. C. for 15 to 60 min. The fibers are dewatered, washed, dewatered, and dried. The heat treatment is said to pasturize the fiber and overcome the natural bacteria in the fiber. The product is suggested for use to enhance the fiber content in bread, pancakes, rolls, and cookies and contribute no more than 0.2 cal/g of fiber.
A common feature of the above described prior art procedures is that in each procedure, the dietary fiber was treated in some way to remove solubles, toxins, phytic acid, improve mouth feel, change color, or increase fiber content. The object of those prior art procedures was to improve an already known natural dietary fiber source in some way and to accept the result. In contrast, a significant modification of fiber is possible via the process disclosed in the J. M. Gould and L. E. Dexter U.S. Pat. No. 4,774,098 for making a dietary fiber from plant straw. In the patented process essentially all the lignin in the plant straw is removed leaving cellulose/hemicellulose as the dietary fiber. The process is based on an alkalinehydrogen peroxide treatment of the lignocellulose at pH 11.2 to 11.8 at ambient temperatures in which the material is delignified and the remaining cellulose and hemicellulose are made available to ruminants. When the lignin is removed, a white product, referred to as a modified plant fiber, is obtained which can be used as a non-caloric substitute for cereal flour. The process converts a waste agricultural lignocellulose from non-wood plants into a more desirable natural dietary fiber for incorporation in wide variety of foods, such as bread, cakes, cookies, etc.
Many foods to which dietary fiber might be added contain unsaturated fatty acids in a triglyceride molecule which are easily oxidized by 0.sub.2, so that the food can become rancid on standing even if the fat content is quite low such as 1 or 2%. The oxidized products are volatile aldehydes and ketones that impart the rancid taste and odor. The presence of metals such as Fe or Cu, act to accelerate the oxidation, whereas metal, chelators and chemical antioxidants can retard the oxidation. It would be advantageous if the dietary fiber being added possessed antioxidant activity.
In its simplest form the oxidation of fat or oil proceeds in a multiple step free radical chain reaction. The initiation step is the formation of a fatty acid radical when a proton departs on a-methylene carbon in the unsaturated fatty acid group of a fat molecule (RH). The resulting free radical ##STR1## (R) easily reacts with molecular oxygen (O.sub.2) to give an unstable peroxide radical (ROO) which in turn is very reactive with the fat molecules. The autocatalytic propagation of free radicals account for the sudden increase in oxidation. The details of the complete oxidation process are not understood but an antioxidant (AH) can inactivate or terminate the early propagation of free radical propagation with the effect of delaying the oxidative rancidity. The antioxidant, in effect, is sacrificed to terminate free radical propagation by becoming a very stable, unreactive free radical (A).
Well known and effective chemical antioxidants are hindered phenols such as butylated hydroxyanisole (BHA), butylated hydroxy toluene (BHT), tertiary-butylhydroquinone (TBHQ), and propyl gallate (PG). All these compounds form free radicals when they react with one of the propagating free radicals. Because of the number of mesomeric forms available for the free radical, the radical stability is increased with a corresponding decrease in reactivity. Thus, the antioxidant delays the oxidation of the substrate. The longer the delay the more effective is the antioxidant.
It is known that the use of lignin components from lignocellulose, such as Kraft lignins from paper pulp refining or acid precipitated lignin fraction from microbial degradation products of lignin, can have antioxidant properties in polymers and food.
It also is known that lignin derived components, such as the Kraft lignin from paper pulp refining, are made up of hindered phenols and are effective as antioxidants in rubber. There are other indications that lignin or its derivatives have antioxidant properties. For example, it has been reported that when 2.5 wt% Indulin AT, a lignin sulfonic acid derived from paper pulp delignification, is added to stripped corn oil, it gives the same antioxidant protection as 0.03 wt% and 6 tocopherol, a natural antioxidant. In contrast, 2.5 wt% addition of pure cellulose to stripped corn oil gives no antioxidant protection. It was recently reported that 0.5 wt% of the lignin isolated by enzymatic hydrolysis of the protein and cellulose from ground carrots can protect the methyl ester of sunflower oil from autoxidation.
An advanced approach to produce lignin derived antioxidants is disclosed in the Crawford and Pometto U.S. Pat. No. 4,478,747. In the patented process any natural occurring lignin from grasses, plants, or trees can be incubated up to 8 weeks with Streptomyces sp., which are known lignin degraders, to produce a water soluble acid precipitable polymeric degraded lignin (APPL) which has antioxidant properties in food, fuel oils, plastics, rubber, etc. Improved antioxidant properties of APPL are achieved by further chemical treatment. For example, the best APPL at 0.1 mg per gram of safflower oil gave 3 to 4.5 days of delay in autoxidation tests compared to 8 days for BHA and 2 days with no antioxidant.
In addition, in the Namiki et al. U.S. Pat. No. 4,649,206 a dilignol compound derived by treating crushed sesame seeds with b-glucosidase is reported to give antioxidant protection to pure linoleic acid.
Since some hindered phenolic compounds are antioxidants, it is reasonable to expect that the breakdown of native lignin, such as the lignocellulose present in many dietary fibers, could produce a host of hindered phenolic compounds such as ferulic, vanillic, syringic, a P-hydroxy benzoid acids, which might contribute antioxidant properties to the dietary fiber.
In the known prior art techniques of producing antioxidants from lignocellulose, the lignin has been removed as chemically modified fragments from the lignocellulose.
It would be advantageous to have a method by which lignocellulosic plant fiber, such as cereal bran, could be simply converted to a dietary fiber with enhanced functional and antioxidant properties.